I just installed electronic ignition in my 1975 914. Now the idle is way high. I can't seem to find any clear explanation as to how to set idle speed on the D Jetronic fuel system. The Haynes manual is totally useless. Can someone help me figure out how to redue the idle speed?


Alan

There's a thumbscrew on the throttle body, driver's side toward the front of the car.

However, I'd start by checking for intake leaks.

vac line leaks, timing not correct, etc etc

idle screw on throttle body -make sure its not open
AAr valve could be open not closing,
is the hose connected from the throttle body to the vac canister?
there is an idle screw on top of ECU adjusts the rich/lean at idle only.
- common locations for vac leaks are intake runners and plenum.
- make sure you set timing with everyting plugged and the vac canister not hooked up, make sure its set to the correct mark on the fan and at 27'BTDC.

oh and

Since you just replaced ignition and that's when the problem started, check your timing. If it's too advanced it will create high idle. If there's a vacuum retard port, make sure that's been reconnected.

I agree
sounds like your timing isn't quite exactly where it was before

Thanks to all for the quick responses! I will check the timing, then look for vacuum leaks. I have yet to find that screw on the throttle body! I assume the throttle body is the assembly under the air filter that has the throttle cable attached.

Yes. The screw is towards the back of the car/driver's side. I can reach it without taking the air cleaner off from the passenger side. Making changes there may also require changes on the ECU knob if the idle starts hunting.

Thanks again I found the mixture screw on the intake (don't know how I missed it) I closed it idle went down. I found the ECU box (didn't know what that was!) there is a large "knob" and next to it a screw. Which do I turn for the idle adjustment?

That knob makes a small adjustment on idle mixture. IIRC it's 15 "clicks", and full counter clockwise is the leanest setting and full clockwise is most rich. Again, this is only at idle (your TPS needs to be properly adjusted so the idle circuit "engages" or this has no effect). So the knob doesn't control idle "speed" directly (like bypass screw on TB), but it can have impact when you change the mixture. You'll have to play with it to see what your engine wants, but go in slow increments (1 or 2 clicks). You also may want to count how many clicks back to full lean (or rich) so you know where you are currently.

Great! Many thanks for your help! I think I got this wrapped up now.